1. Field of the Invention
The present invention relates to a power turbine for a turbine engine. More specifically, the present invention relates to the use of a combination power turbine and flywheel assembly for a dual shaft turbine engine.
2. Description of the Related Art
Liquid fueled turbine engines have been used to power vehicles because of their operating efficiency and durability. They are especially useful when used at a constant speed and under a constant vehicle load. Operating a turbine engine at a constant speed and load greatly extends the durability of the engine and optimizes its fuel efficiency. Turbine engines may be directly coupled to the vehicle drive wheels to provide a mechanical drive or, alternatively, they maybe used to operate a generator to provide electric drive.
It is known to use a turbine engine to directly power the drive wheels of a vehicle as illustrated in U.S. Pat. No. 4,157,011, issued Jun. 5, 1979, to Liddle. The Liddle patent teaches the use of a single shaft turbine engine mechanically coupled through a continuously variable transmission to the vehicle drive wheels. The engine is used in an intermittent fashion and requires repeated restarts. A flywheel located between the turbine and the transmission provides a rotational inertia that is sufficient to start turbine engine. An optional clutch allows the turbine engine to be switched on and off. The vehicle may be manually driven for a short period of time on the inertia of the flywheel once the turbine engine is shut down. The primary disadvantages of this system are the limitations of continuously variable transmissions to transmit mechanical energy. Heavy vehicle load requirements, such as the torque needed to power the vehicle up hills or over obstacles, are transmitted through the transmission and to the turbine engine. This creates a load or drag on the engine and thereby reduces the engine's operating efficiency. Additionally, frictional forces within the continuously variable transmission significantly reduce the operating efficiency of the propulsion system. These and other disadvantages of mechanically coupling the engine to the drive wheels has led others to indirectly couple the turbine engine to the vehicle wheels.
To maintain the efficiency of a turbine engine, it has been used to power a generator. The generator in turn powers a vehicle traction motor that operates the drive wheels. A system that used this approach is illustrated in U.S. Pat. No. 4,336,856, issued Jun. 29, 1982, to Gamell. Like the Liddle patent, the Gainell patent teaches a single shaft turbine engine directly coupled to a generator/motor. The generator/motor in turn provides electrical current to power a vehicle traction motor. The motor drives the vehicle wheels. An optional clutch between the turbine engine and generator/motor permits the turbine to rotate freely when the vehicle is stopped. By releasing the clutch, the vehicle can be started up slowly.
A flywheel attached adjacent the drag turbine provides additional rotational inertia to the turbine engine. Single shaft turbine engines, as the type used in Gamell, suffer from the problem of transmitting vehicle drag to the turbine engine when the vehicle is under a significant load. This drag causes an increased torque on the turbine engine, thereby reducing the engine operating efficiency.
The flywheel taught by Gamell exposes the rotating flywheel to ambient air. The air drag on the rotating flywheel reduces the flywheel efficiency and thus, the overall efficiency of the vehicle. Others have used flywheels contained within a vacuum enclosure to reduce the air drag on the flywheel. These systems have required gearing to match the flywheel rotational speed to that of the engine.
It is desirable to provide a power turbine flywheel assembly that has a reduced air drag on the flywheel without the need of a vacuum enclosure. It is a further desire of the present invention to provide a flywheel assembly for a dual shaft turbine engine that is compact and easy to manufacture. It is yet another desire of the present invention to reduce the number of bearings needed to support a power turbine and flywheel. These and other advantages and features of the present invention would be more fully described below and in the accompanying drawings.